The present invention relates to an optical recording medium, particularly to an optical recording medium capable of recording and reproducing information with a high density by virtue of a laser beam having a short wavelength.
For recording and reproducing information with a high density, there have been developed some new optical recording mediums capable of recording and reproducing information with the use of a laser beam having a wavelength shorter than 780 nm. Such optical recording mediums each comprises a substrate layer and a recording layer formed on the substrate layer. The substrate layer is formed with a plurality of grooves and has a plurality of prepits (containing address information) formed and arranged circumferentially at a predetermined interval between the grooves.
Further, for information recording and reproducing with a high density, sufficient research has been made on a relationship between the shapes of the grooves, prepits and a laser beam having a wavelength near 780 nm. However, there still have not been any sufficient research on how to contract a track pitch and how to converge a short wavelength laser beam in order for an optical recording medium to record and reproduce information with a high density.
Usually, an optical recording medium is adapted to record information by forming a plurality of small recording areas, making use of an optical characteristic variation on a recording layer. However, if a track pitch is contracted from a conventional size (1.6 .mu.m) to a smaller size (1 .mu.m or lower) in order to effect a high density recording and reproducing, there will occur a problem of cross talk. Further, the shapes of grooves and prepits formed in accordance with a conventional designing, when used for high density information recording and reproducing, will bring some undesirable influences to the quality of signals reproduced from the small recording areas.